Electrochromic medium having a color stability

ABSTRACT

An electrochromic window assembly is disclosed that includes a first substrate and a second substrate that is maintained in a parallel and spaced relation from the first substrate by means of a window frame and spacer. The window assembly further includes an electrochromic device mounted within the airtight chamber formed between the first and second substrates. Electrochromic device  22  may be mounted so as to provide an air chamber between first substrate  12 , which is the external substrate, and electrochromic device  22 . At least one of the chambers formed between substrates  12  and  14  and electrochromic device  22  may be filled with an insulating gas such as argon. Also disclosed are novel methods for manufacture of an electrochromic device for incorporation into such a window assembly. A novel electrochromic device is also disclosed having electrical bus clips secured about the entire periphery of the electrochromic device. Also disclosed is the use of steel bus clips for the electrochromic device.

BACKGROUND OF THE INVENTION

The present invention generally relates to windows having variabletransmittance light filters, and more specifically to windows includingelectrochromic light filters.

Variable transmittance light filters, such as electrochromic lightfilters, have been proposed for use in architectural windows, skylights,and in windows and sunroofs for automobiles. Such electrochromic lightfilters reduce the transmittance of direct or reflected sunlight duringdaytime through the window, while not reducing such transmittance duringnighttime. Not only do such light filters reduce bothersome glare andambient brightness, but they also reduce fading of interior materialsand heat load caused by the transmittance of sunlight through thewindow.

Electrochromic windows have not been widely accepted commercially forseveral reasons. First, they tend to be very expensive due to the costof materials required for their construction, and their complexconstruction makes mass production difficult. Additionally,electrochromic windows have tended to have a lower life expectancy thanconventional windows due to degradation of the electrochromic materialsused in the window. The combination of added cost and lower lifeexpectancy have deterred many architects and builders from usingelectrochromic windows.

SUMMARY OF THE INVENTION

Accordingly, an aspect of the present invention is to provide animproved electrochromic window construction. More specifically, anaspect of the invention is to provide an electrochromic window that iseasier to mass-produce and that utilizes less expensive components andlower quantities of the costlier components. Another aspect of thepresent invention is to provide an electrochromic window that exhibitsmarkedly improved color stability. Still another aspect of the presentinvention is to provide an electrochromic window having improved thermaldeflection/emission characteristics. Yet another aspect of the inventionis to provide an electrochromic window having an improved sealconstruction.

To achieve these and other aspects and advantages a window of oneembodiment of the present invention comprises a first substrate, asecond substrate, a spacer for spacing and maintaining the first andsecond substrates in a generally parallel, spaced-apart relation, and avariable-transmittance device disposed between and spaced apart from thefirst and second substrates thereby defining a first chamber between thefirst transparent element and the variable-transmittance device, and asecond chamber between the second transparent element and thevariable-transmittance device. The variable-transmittance device ispreferably an electrochromic device.

Another embodiment of the invention pertains to a method of making anelectrochromic device that comprises the steps of (1) providing anassembly including a first substrate and a second substrate spaced apartand joined by a seal to form a sealed chamber between inner surfaces ofthe substrates, at least (or both) one of the first and secondsubstrates including an aperture extending between the outer surface ofthe substrate and the chamber; (2) filling the chamber with anelectrochromic solution or an electrolytic solution through theaperture; (3) placing a plug in the aperture; and (4) adhering a thinplate over the plugged aperture.

Another embodiment of the invention pertains to a method of making anelectrochromic device comprising the steps of (1) providing a firstsubstrate; (2) adhering a first surface of a pre-formed seal gasket ontoa first surface of the first substrate proximate the periphery thereof,the seal gasket having adhesive pre-applied to a second surface oppositethe first surface, and having a release liner attached to the adhesiveon the second surface of the seal gasket; (3) removing the release linerfrom the second surface of the seal gasket; and (4) aligning a secondsubstrate with the first substrate and pressing a first surface of thesecond substrate onto the adhesive on the second surface of the sealgasket.

According to yet another embodiment, a window of the present inventioncomprises an electrochromic medium having color stability defined as (1)a change in color ΔE of less than 5 measured in its activated ordarkened state after being exposed to 700 hours in a weatherometer whilecycling; and (2) a change in color, ΔE, of less than 5 measured in itsdeactivated or clear state after being exposed to 700 hours in aweatherometer while cycling, each cycle consists of applying a voltageof 1.2V for 20 sec. and 0.0V for 40 sec.

According to still yet another embodiment, a window of the presentinvention comprises a first substrate, a second substrate, a spacer forspacing and maintaining the first and second substrates in a generallyparallel, spaced-apart relation, and first and secondvariable-transmittance devices disposed between the first and secondsubstrates and spaced apart from each other. The variable transmittancedevices are preferably electrochromic devices.

According to another embodiment, an electrochromic device of the presentinvention comprises first and second transparent elements joined by aseal in a parallel, spaced-apart relation to form a chambertherebetween, a first transparent electrode disposed over the innersurface of the first element, a second transparent electrode disposedover the inner surface of the second element, the first and secondelectrodes being electrically isolated from one another, anelectrochromic medium disposed within the sealed chamber, a firstelectrical conductor electrically coupled to the first electrode aboutthe entire perimeter of the first electrode, and a second electricalconductor electrically coupled to the second electrode about the entireperimeter of the second electrode.

According to another embodiment, an electrochromic device of the presentinvention comprises a first substrate and a second substrate spacedapart and joined by a seal to form a sealed chamber between innersurfaces of the substrates, the substrates being positioned to have atleast a first edge generally aligned with the first edge of the othersubstrate, a first electrode disposed on the inner surface of the firstsubstrate, a second electrode disposed on the inner surface of thesecond substrate, the first and second electrodes being electricallyisolated from one another, an electrochromic medium disposed within thesealed chamber, a first electrical connector clip attached to the firstelectrode and to the first substrate along at least the first edgethereof, and a second electrical connector clip attached to the secondelectrode and to the second substrate along at least the first edgethereof, wherein the first and second electrical connector clips includea plurality of spaced-apart fingers that respectively contact the firstand second electrodes, the fingers of one connector clip being spacedapart from one another by a distance greater than the width of thefingers of the other connector clip such that the fingers of the boththe connector clips intermesh without physically contacting the fingersof the other connector clip. The clips may be made of steel.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1A is a cross-sectional view of a portion of an electrochromicwindow constructed in accordance with a first embodiment of the presentinvention;

FIG. 1B is a side view of a portion of the electrochromic window shownin FIG. 1A;

FIG. 2A is a cross-sectional view of a portion of an electrochromicwindow constructed in accordance with a second embodiment of the presentinvention;

FIG. 2B is a cross-sectional view of a portion of a modified version ofthe electrochromic window shown in FIG. 2A;

FIG. 3A is a cross-sectional view of a portion of an electrochromicwindow constructed in accordance with a third embodiment of the presentinvention;

FIG. 3B is a cross-sectional view of a portion of a modified version ofthe electrochromic window shown in FIG. 3A;

FIG. 4A is a cross-sectional view of a portion of an electrochromicwindow constructed in accordance with a fourth embodiment of the presentinvention;

FIG. 4B is a cross-sectional view of a portion of a modified version ofthe electrochromic window shown in FIG. 4A;

FIG. 5 is a perspective view of a first subassembly used to construct anelectrochromic device in accordance with one embodiment of the presentinvention;

FIG. 6A is a cross-sectional view of the first subassembly shown in FIG.5 taken along line 6-6′;

FIG. 6B is a cross-sectional view showing a second step in the inventivemethod for assembling an electrochromic device;

FIG. 6C is a cross-sectional view showing a third step in the inventivemethod for assembling an electrochromic device;

FIG. 6D is a cross-sectional view showing a fourth step in the inventivemethod for assembling an electrochromic device;

FIG. 6E is a cross-sectional view showing a fifth step in the inventivemethod for assembling an electrochromic device;

FIG. 6F is a cross-sectional view showing a sixth step in the inventivemethod for assembling an electrochromic device;

FIG. 6G is a cross-sectional view showing a seventh step in theinventive method for assembling an electrochromic device;

FIG. 6H is a side perspective view of a partially assembledelectrochromic device constructed in accordance with the inventivemethod;

FIG. 6I is a cross-sectional view showing an eighth step in theinventive method for assembling an electrochromic device;

FIG. 7 is a cross-sectional view of a portion of an electrochromicdevice constructed in accordance with another embodiment of the presentinvention;

FIG. 8 is a cross-sectional view of a portion of an electrochromicdevice constructed in accordance with yet another embodiment of thepresent invention;

FIG. 9 is a cross-sectional view of a portion of an electrochromicwindow assembly constructed in accordance with another embodiment of thepresent invention;

FIG. 10A is a side perspective view of a partially assembledelectrochromic device constructed in accordance with the inventivemethod;

FIG. 10B is a front view of a portion of the device shown in FIG. 10A;and

FIG. 10C shows end and side perspective views of a bus clip constructedin accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numeralswill be used throughout the drawings to refer to the same or like parts.

FIG. 1A shows the construction of an electrochromic window assembly 10according to a first embodiment of the present invention. As shown,electrochromic window assembly 10 includes a first transparent substrate12 and a second spaced-apart and parallel second transparent substrate14. A frame (not shown) may be provided about the outer periphery ofsubstrates 12 and 14 and about a portion of the external surface 12 a offirst substrate 12 and the internal surface 14 b of second substrate 14.Transparent substrates 12 and 14 may be made of tempered glass,annealed, heat, or chemically strengthened or laminated glass or othertransparent material. Spacing between substrates 12 and 14 is maintainedby a spacer 18. Spacer 18 may be made of wood or aluminum, butyl, EPDM,silicone or other rubbers, steel, or virtually any, durable material.Spacer 18 preferably includes a groove 20 for supporting anelectrochromic device 22 in a spaced-apart and parallel position betweenfirst substrate 12 and second substrate 14.

As illustrated with respect to the first embodiment shown in FIG. 1A,electrochromic device 22 is preferably positioned closer to firstsubstrate 12 than to second substrate 14. Locating an electrochromicdevice 22 closer to the outer substrate of a window provides the mostenergy efficient construction. While in later embodiments it is proposedto integrate the electrochromic device with the first substrate suchthat there is no spacing therebetween so as to maximize energyefficiency, the first embodiment includes a first chamber 24 that isdefined between first substrate 12 and electrochromic device 22. Byspacing electrochromic device 22 from first substrate 12, resultantchamber 24 may buffer wind loading on electrochromic device 22. Further,greater flexibility is achieved in the design and material selection offirst substrate 12 by not utilizing first substrate 12 as an integralelement of electrochromic device 22. In other words, first substrate 12may be made of materials that are otherwise not suitable to serve as anintegral element of and electrochromic device. For example, firstsubstrate 12 may be made of tempered glass or other materials that arenot flat.

A second chamber 26 is similarly provided between electrochromic device22 and second inner substrate 14. To provide for thermal insulation,second chamber 26 may be filled with a gas such as argon. Similarly,first chamber 24 may be filled with the same gas or, alternatively, witha different gas. For example, first chamber 24 may be filled with a gashaving a higher thermal conductivity, such as helium, air, or nitrogen,which all have higher thermal conductivities than argon, which wouldpreferably be provided in the second chamber 26. In this manner, solarenergy from the sun is absorbed by the electrochromic device 22 (when ina darkened state), and the heat that is generated through thisabsorption is quickly transmitted via the gas in first chamber 24 backthrough first substrate 12 to the exterior of the window and henceoutside the building. On the other hand, by providing an insulating gassuch as argon in second chamber 26, the generated heat may be insulatedfrom second substrate 14, and hence, the interior of the building.Chamber 24 can also serve as a UV blocking layer by the use of a UVabsorber. Use of an absorber in solution or in a gel would also improvethe thermal coupling between the electrochromic device and the outside.

With respect to the first through fourth embodiments, electrochromicdevice 22 may have any known construction including, for example, any ofthe constructions disclosed in U.S. patent application Ser. No.09/343,345 entitled ELECTRODE DESIGN FOR ELECTROCHROMIC DEVICES, filedon Jun. 30, 1999, by Thomas F. Guarr et al., and U.S. Pat. No.5,805,330, the entire disclosures of which are incorporated herein byreference.

Preferred alternative constructions are nevertheless described belowwith respect to FIGS. 5, 6A-6I, 7, and 8.

In general, electrochromic device 22 may include a first transparentelement 28, a second transparent element 30, a first transparentelectrode layer 32 applied to an inward-facing surface of firsttransparent element 28, a second transparent electrode 34 applied to aninward-facing surface of second transparent element 30, and a first seal36 provided between the two layered transparent substrates. Transparentelements 28 and 30 are maintained in a generally parallel spaced-apartrelation. Seal 36 serves to provide a chamber between elements 28 and 30in which an electrochromic medium 38 is contained in contact with bothtransparent electrodes 32 and 34. Electrochromic medium 38 includeselectrochromic anodic and cathodic materials that can be grouped intothe following categories:

(i) Single layer—the electrochromic medium is a single layer of materialwhich may include small inhomogeneous regions and includessolution-phase devices where a material is contained in solution in theionically conducting electrolyte and remains in solution in theelectrolyte when electrochemically oxidized or reduced. U.S. patentapplication Ser. No. 09/034,531 entitled “NEAR INFRARED-ABSORBINGELECTROCHROMIC COMPOUNDS AND DEVICES COMPRISING SAME”, now U.S. Pat. No.6,193,912; U.S. patent application Ser. No. 09/377,455 entitled “COLORSTABILIZED ELECTROCHROMIC DEVICES”, now U.S. Pat. No. 6,188,505; U.S.patent application Ser. No. 09/454,043 entitled “ANODIC ELECTROCHROMICMATERIAL HAVING A SOLUBILIZING MOIETY”, now U.S. Pat. No. 6,262,832;U.S. patent application Ser. No. 09/302,866 entitled “ELECTROCHROMICMEDIA WITH CONCENTRATION ENHANCED STABILITY PROCESS FOR PREPARATIONTHEREOF AND USE IN ELECTROCHROMIC DEVICE”; U.S. patent application Ser.No. 09/366,115 entitled “ELECTROCHROMIC MATERIALS WITH ENHANCEDULTRAVIOLET STABILITY”, now U.S. Pat. No. 6,195,192; U.S. patentapplication Ser. No. 09/677,689 [Attorney Docket No. AUTO 818] entitled“SUBSTITUTED METALLOCENES FOR USE AS AN ANODIC ELECTROCHROMIC MATERIALAND ELECTROCHROMIC MEDIA AND DEVICES COMPRISING SAME”; and U.S. patentapplication Ser. No. 09/350,879 entitled “COUPLED ELECTROCHROMICCOMPOUNDS WITH PHOTOSTABLE DICATION OXIDATION STATES”, now U.S. Pat. No.6,249,369, disclose anodic and cathodic materials that may be used in asingle layer electrochromic medium, the entire disclosures of which areincorporated herein by reference. Solution-phase electroactive materialsmay be contained in the continuous solution phase of a cross-linkedpolymer matrix in accordance with the teachings of U.S. Pat. No.5,928,572, entitled “IMPROVED ELECTROCHROMIC LAYER AND DEVICESCOMPRISING SAME” or International Patent Application No. PCT/US98/05570entitled “ELECTROCHROMIC POLYMERIC SOLID FILMS, MANUFACTURINGELECTROCHROMIC DEVICES USING SUCH SOLID FILMS, AND PROCESSES FOR MAKINGSUCH SOLID FILMS AND DEVICES,” the entire disclosures of which areincorporated herein by reference.

At least three electroactive materials, at least two of which areelectrochromic, can be combined to give a pre-selected color asdescribed in U.S. Pat. No. 6,020,987 entitled “ELECTROCHROMIC MEDIUMCAPABLE OF PRODUCING A PRE-SELECTED COLOR,” the entire disclosure ofwhich is incorporated herein by reference. This ability to select thecolor of the electrochromic medium is particularly advantageous whendesigning architectural windows.

The anodic and cathodic materials can be combined or linked by abridging unit as described in International Application No.PCT/WO97/EP498 entitled “ELECTROCHROMIC SYSTEM,” the entire disclosureof which is incorporated herein by reference. It is also possible tolink anodic materials or cathodic materials by similar methods. Theconcepts described in these applications can further be combined toyield a variety of electrochromic materials that are linked.

Additionally, a single layer medium includes the medium where the anodicand cathodic materials can be incorporated into the polymer matrix asdescribed in International Application No. PCT/WO98/EP3862 entitled“ELECTROCHROMIC POLYMER SYSTEM,” U.S. Pat. No. 6,002,511, orInternational Patent Application No. PCT/US98/05570 entitled“ELECTROCHROMIC POLYMERIC SOLID FILMS, MANUFACTURING ELECTROCHROMICDEVICES USING SUCH SOLID FILMS, AND PROCESSES FOR MAKING SUCH SOLIDFILMS AND DEVICES,” the entire disclosures of which are incorporatedherein by reference.

Also included is a medium where one or more materials in the mediumundergoes a change in phase during the operation of the device, forexample, a deposition system where a material contained in solution inthe ionically conducting electrolyte which forms a layer, or partiallayer on the electronically conducting electrode when electrochemicallyoxidized or reduced.

(ii) Multilayer—the medium is made up in layers and includes at leastone material attached directly to an electronically conducting electrodeor confined in close proximity thereto which remains attached orconfined when electrochemically oxidized or reduced. Examples of thistype of electrochromic medium are the metal oxide films, such astungsten oxide, iridium oxide, nickel oxide, and vanadium oxide. Amedium, which contains one or more organic electrochromic layers, suchas polythiophene, polyaniline, or polypyrrole attached to the electrode,would also be considered a multilayer medium.

In addition, the electrochromic medium may also contain other materials,such as light absorbers, light stabilizers, thermal stabilizers,antioxidants, thickeners, or viscosity modifiers.

It may be desirable to incorporate a gel into the electrochromic deviceas disclosed in commonly assigned U.S. Pat. No. 5,940,201 entitled “ANELECTROCHROMIC MIRROR WITH TWO THIN GLASS ELEMENTS AND A GELLEDELECTROCHROMIC MEDIUM,” filed on Apr. 2, 1997. The entire disclosure ofthis U.S. patent is incorporated herein by reference.

First and second transparent elements 28 and 30 may be any materialwhich is transparent and has sufficient strength to be able to operatein the environmental conditions to which the device will be exposed.Elements 28 and 30 may comprise any type of borosilicate glass, sodalime glass, float glass, or any other material, such as, for example,MYLAR®, polyvinylidene chloride, polyvinylidene halides, such aspolyvinylidene fluoride, a polymer or plastic, such as cyclic olefincopolymers like Topas® available from Ticona, LLC of Summitt, NewJersey, that is transparent in the visible region of the electromagneticspectrum. Elements 28 and 30 are preferably made from sheets of glass.

Additionally, substrates 12 and 14 may be treated or coated as isdescribed in U.S. patent application Ser. No. 09/200,625 entitled“ELECTROCHROMIC STRUCTURES,” now U.S. Pat. No. 6,239,898, U.S. patentapplication Ser. No. 09/435,266 entitled “AN ELECTROCHROMIC DEVICEHAVING A SELF-CLEANING HYDROPHILIC COATING,” now U.S. Pat. No.6,193,378, and U.S. patent application Ser. No. 09/602,919 [AttorneyDocket No. GEN10P372] entitled “AN ELECTRO-OPTIC DEVICE HAVING ASELF-CLEANING HYDROPHILIC COATING,” filed on Jun. 23, 2000, the entiredisclosures of which are incorporated herein by reference. Othertreatments, such as anti-reflectance coatings, hydrophilic coatings,low-E coatings, and UV-blocking layers are also envisioned. Also, suchcoatings may be applied to elements 28 and 30 in this and otherembodiments.

Transparent electrodes 32 and 34 may be made of any material which bondswell to transparent elements 28 and 30, is resistant to corrosion to anymaterials within the electrochromic device, resistant to corrosion bythe atmosphere, has minimal diffuse or specular reflectance, high lighttransmission, near neutral coloration, and good electrical conductance.Transparent electrodes 32 and 34 may be fluorine-doped tin oxide, dopedzinc oxide, zinc-doped indium oxide, tin-doped indium oxide (ITO),ITO/metal/ITO (IMI) as disclosed in “Transparent ConductiveMultilayer-Systems for FPD Applications,” by J. Stollenwerk, B. Ocker,K. H. Kretschmer of LEYBOLD AG, Alzenau, Germany, the materialsdescribed in above-referenced U.S. Pat. No. 5,202,787, such as TEC 20 orTEC 15, available from Libbey Owens-Ford Co. of Toledo, Ohio, or othertransparent conductors. Generally, the conductance of transparentelectrodes 32 and 34 will depend on their thickness and composition. IMIgenerally has superior conductivity compared with the other materials.IMI, however, is known to undergo more rapid environmental degradationand suffer from interlayer delamination. The thickness of the variouslayers in the IMI structure may vary, but generally the thickness of thefirst ITO layer ranges from about 10 Å to about 200 Å, the metal rangesfrom about 10 Å to about 200 Å, and the second layer of ITO ranges fromabout 10 Å to about 200 Å. If desired, an optional layer or layers of acolor suppression material may be deposited between transparentelectrodes 32 and 34 and the inner surface of element 28 to suppress thetransmission of any unwanted portions of the electromagnetic spectrum.

In the particular embodiment shown in FIG. 1A, seal 36 may be anymaterial that is capable of adhesively bonding to the coatings on theinner surfaces of transparent elements 28 and 30 to seal the perimeter,such that electrochromic material 38 does not leak from the chamberdefined between the transparent substrates. The seal preferably has goodadhesion to glass, metals, and metal oxides; preferably has lowpermeabilities for oxygen, moisture vapor, and other detrimental vaporsand gasses; and must not interact with or poison the electrochromicmaterial it is meant to contain and protect. The seal may be applied inany conventional manner. A preferred seal material and method forapplying the seal as well as a preferred method of constructingelectrochromic device 22 are described further below.

As illustrated in FIG. 1A, electrochromic device 22 further includes apair of electrical bus clips 40 a and 40 b that are respectively clippedabout the perimeter of first and second transparent elements 28 and 30in such a manner as to physically and electrically contact transparentelectrodes 32 and 34. Bus clips 40 a and 40 b thus enable electricalcurrent to flow between an external driving circuit through first andsecond transparent electrodes 32 and 34 and the electrochromic medium 38contained in the chamber therebetween. In this manner, the lighttransmittance of electrochromic device 22 may be varied in response toelectrical control of an external drive circuit. Bus clips 40 a and 40 bmay be made of any known construction and known materials. One possibleconstruction for bus clips 40 a and 40 b is disclosed in U.S. patentapplication Ser. No. 08/917,643 entitled “AN IMPROVED CLIP FOR USE WITHTRANSPARENT CONDUCTIVE ELECTRODES IN ELECTROCHROMIC DEVICES” filed onAug. 22, 1997, by Tonar et al., now U.S. Pat. No. 6,064,509, thedisclosure of which is incorporated herein by reference. Preferredconstructions for bus clips 40 a and 40 b, as well as preferredmaterials for the bus clips, are described further below.

Other novel configurations for bus clips would include the use of twobus clips that were held together by an insulating, non-conductivematerial such as a plastic or rubber. This arrangement would allow thebus clips to be attached to both opposing glass elements 28 and 30 inone step without allowing them to short each other out electrically. SeeFIG. 6H.

Again, bus clips are used as a means of uniformly transferringelectricity from lead wires to the conductive coating that has beenpreviously deposited on the glass elements. This can also beaccomplished by the use of a metal-doped paint or coating (such assilver, copper, etc.), or by the use of conductive adhesive tapes, suchas those available from the 3M Corporation. Examples of these tapes are3M's Electrically Conductive Adhesive Transfer Tape #9703 and #9713.Additionally, metal foil or exposed wire may be used.

As illustrated in FIG. 1A, a second seal in the form of a sealant 42 isapplied within any gaps that may exist between the perimeter ofelectrochromic device 22 and groove 20. As described further below,sealant 42 may be an epoxy or the like that can readily flow within thesmall void areas surrounding clips 40 within groove 20.

A third seal in the form of a sealant 44 is also provided between spacer18 and first and second substrates 12 and 14 and frame 16. Sealant 44 isprovided to ensure that the chambers 24 and 26 between substrates 12 and14 are airtight such that any gasses that may be contained in chambers24 and 26 may not leak out from between substrates 12 and 14. Sealant 44further serves as a moisture barrier for preventing moisture from theenvironment surrounding the window from reaching the chambers betweensubstrates 12 and 14.

The sealants 18, 42, and 44 may be a hot melt rubber compound, such as ahot melt butyl, a silicone, a urethane, a polysulfide, or the like.Additionally, the sealants 18, 42, and 44 may be modified for aesthetic,chemical, or physical properties by the use of various additives. Theseadditives may include, but are not limited to, anti-oxidants, pigments,rheology modifiers, fibers, glass and synthetic spheres, and the like.

The window assembly 10 shown in FIG. 1A may include one or more layers46 applied to one of the surfaces of substrate 12, substrate 14, and/oreither surface of electrochromic device 22. Such layers may include alow-emission (low-E) layer or stack, a heat mirror, an ultraviolet (UV)filter of blocking layer, and a near infrared (NIR) blocking layer orfilter.

The placement of the layer 46 will vary, depending on the function it isto perform. If a UV filter is used, it would be disposed on surface 12a, 12 b or 22 a in order to block UV radiation from reachingelectrochromic device 22. If the UV filter is placed on surface 12 a,protection in the form of a hard coat would also be provided. Since theelectrochromic device would absorb a significant amount of solarradiation, the placement of the low-E coating would be somewhatdifferent than commonly used in insolated glass units (IGUs) currentlyavailable. The electrochromic device 22 in its darkened state insunlight would become the portion of the window that has the highesttemperature, therefore any low-E coatings would be most useful inside ofthe electrochromic device 22 to reject heat during the summer months.The low-E coating would be disposed on surfaces 22 b, 14 a, or 14 b,with 22 b giving the best rejection of heat from the outside, again ifsurface 14 b is coated with a low-E coating, an additional hardcoatcould also be provided. The NIR filter, if it absorbs NIR radiation,would be heated by sunlight and for heat rejection would preferably beplaced on one of the surfaces of substrate 12 or on surface 22 a.Additionally, if the low-E coating were disposed on substrate 14, an NIRabsorbing filter could be placed on surface 22 b.

As illustrated in FIGS. 1A and 1B, window assembly 10 may furtherinclude one or more channels 48 formed in spacer 18 that extend from oneside of electrochromic device 22 to the other side and thereby allowairflow between first chamber 24 and second chamber 26. By allowing suchairflow between the chambers, the affects of wind loading on device 22may be reduced. Such wind loading causes substrate 12 to bow inward,causes the gas contained in a airtight chamber 24 to compress, andthereby causes electrochromic device 22 to also be affected by windloading. Channel(s) 48 equalize the pressures on either side ofelectrochromic device 22 and thereby reduces any flexing of thetransparent substrates or other components of electrochromic device 22as a result of wind loading. Such air passage between channels 24 and 26also would reduce temperature loading that may otherwise occur, whichwould again cause an increase of pressure in the gas in the firstchamber 24 without otherwise producing an equal increasing pressure insecond chamber 26. Clearly, if different gasses are maintained inchambers 24 and 26, one would not utilize channel(s) 48.

As shown in FIG. 1A, first seal 36 is protected from the environmentoutside of the window by second seal 42, spacer 18, third seal 44, andframe 16. The sealant used to form third seal 44 is preferably highlyresistant to air and moisture such that the space between substrates 12and 14 is completely airtight. When chambers 24 and 26 are filled withan inert gas such as argon, the material selected for first seal 36 andsecond seal 42 need not be oxygen impermeable or even moistureimpermeable. Nevertheless, first seal 36 must not interact with orpoison the electrochromic medium 38. By removing the requirements thatfirst seal 36 need be oxygen and moisture impermeable, seal 36 may beconstructed using materials not currently used in the construction ofelectrochromic devices. That is, since the inner most (“primary”) sealessentially need only contain the electrochromic fluid or gel, whereasthe secondary seal is more importantly an oxygen and moisture vaporbarrier, the material out of which the inner most seal is constructedcan be selected from a wide range of materials. This allows the primaryseal to be made out of less expensive materials. These materials can bepolyisoprene, polyisobutylene, polychloroprene, ethylene propylene dienemethylene rubbers, polyetheylenes, fluorocarbon rubbers, siliconerubbers, epoxies, polurethanes, nitrites, butyl rubber, neoprene,Teflon® (tetrafluoroethylene fluorocarbon, fluorinatedethylene-propylene, or copolymers thereof) and the like. Additionally,these materials may be modified with different additives to affect thechemical, physical, or their aesthetic appearance. For example, blackpigments could be used to produce a dark sealant, and fumed silica couldbe used to increase thixotropy or adjust the CTE, such as is describedin U.S. Application Pat. No. 09/158,423, filed on Sep. 21, 1998, nowU.S. Pat. No. 6,157,480, the entire disclosure of which is incorporatedherein by reference.

The epoxy seals currently used in constructing electrochromic mirrorsare often thermally cured epoxies. Because electrochromic windows aremuch larger than the rearview mirror, the thermal energy that would berequired to thermally cure the epoxy would be extremely large. Also, theepoxy seals previously used are relatively brittle after curing.Additionally, while such an epoxy works well for smaller electrochromicdevices, such as electrochromic rearview mirrors for automobiles, whensuch an epoxy is used for larger scale electrochromic devices such aswindows, there is great difficulty in maintaining the two transparentelements 28 and 30 in a parallel spaced-apart relation throughout theentire surface area of the electrochromic device, particularly when theepoxy is not firm enough to maintain the spacing until it has time tocure. Because seal 36 is sufficiently protected from the externalenvironment and would only be exposed to the electrochromic medium 38and an inert gas between substrates 12 and 14, first seal 36 may be madeof a material that need not be cured, such as a butyl rubber, silicone,EPDM, polyisobutylene, Teflon, neoprene, viton, or the like. Thus, firstseal 36 may serve as a spacer both during and after the manufacture ofthe electrochromic device. Because seal 36 may be made with a stablematerial, the manner in which such an electrochromic device ismanufactured may be advantageously modified as discussed further belowand thereby provide for a much simpler and inexpensive method ofmanufacture that further facilitates mass-production of such large-scaleelectrochromic devices.

FIG. 2A shows an electrochromic window assembly 100 constructed inaccordance with a second embodiment of the present invention. As will beapparent to those skilled in the art, the second embodiment is similarto the first embodiment with the exception that electrochromic device 22is disposed between two separate spacers 118 a and 118 b. Such aconstruction still allows for the provision of the electrochromic device22 within an airtight chamber between substrates 12 and 14. Oneadvantage to this construction is that it allows for the seal and spacerregion around the periphery of the window unit to have a lower profilethan in the construction shown in FIG. 1A. FIG. 2B shows a modifiedversion of the second embodiment wherein spacers 118 a and 118 b arereplaced with a single spacer 18 and wherein the bottom edges of spacer18 is tapered so as to hide seal 36.

FIG. 3A shows an electrochromic window construction 120 according to athird embodiment of the present invention. Window 120 differs from thewindows of the previous embodiments in that the electrochromic device isformed adjacent first substrate 12 with no chamber formed therebetween.Nevertheless, a chamber is still provided between electrochromic device22 and the inside second substrate 14 that may be an airtight chamberfilled with an insulating gas such as argon or the like. Windowconstruction 120 further may differ from the prior embodiments byeliminating first transparent element 28 and instead applying firsttransparent electrode 32 on a surface of first transparent substrate 12.By eliminating transparent element 28 and by positioning theelectrochromic medium 38 closer to external substrate 12, the windowassembly is not only lighter and less complex, but the heat rejection ofthis construction is enhanced. If preassembly of the electrochromicdevice 22 is desired, a thin transparent sheet of glass, Mylar, oranother plastic material may be used as a first transparent element 28and subsequently adhered to the surface of transparent substrate 12.Such a thin transparent sheet could also be used for element 30. Thelayer 46 in this embodiment would have similar placement with surface 12b and 22 a acting as if they had been merged into a single surface.

To make electrical connection with the two transparent electrodes 32 and34, an electrically conductive bus clip 40 b may be utilized to contactsecond transparent electrode 34 while electrical contact may be madewith first transparent electrode 32 by means of an electrical conductor122 in the form of an exposed wire or metal foil. Conductor 122 may bepressed against first transparent electrode 32 outside of first seal 36and then covered with the insulated glass unit spacer 124.Alternatively, as shown in FIGS. 7 and 8, the electrical conductor maybe disposed between first seal 36 and transparent electrode 32. Furtherstill, as shown in FIG. 3B, transparent electrode 32 may extend upbeyond third seal 44 where contact is made with a conductive clip 122 bon the outside of the airtight chamber formed between substrates 12 and14.

As illustrated in FIG. 3A, seal 36 is still advantageously maintainedwithin the airtight chamber between substrates 12 and 14 that is formedby spacer 124 and seal 44. Accordingly, seal 36 may be made withmaterials that facilitate simple and inexpensive manufacture of theelectrochromic device. Again, material requirements are much less due toseal 44.

FIG. 4A shows an electrochromic window assembly 140 constructed inaccordance with a fourth embodiment of the present invention. Theembodiment shown in FIG. 4A differs from the prior embodiments in thatone or more additional electrooptic device(s) 142 is/are provided withinthe airtight chamber defined between substrates 12 and 14. Firstelectrochromic device 22 is preferably positioned as close as possibleor on the inward-facing surface 12 b of first substrate 12 while secondelectro-optic device 142, which may be another electrochromic device, ora polymer dispersed liquid crystal or suspended particle device (SPD),is positioned closer to the second substrate 14. If device 22 and 142are to be formed on the respective surfaces 12 b and 14 a of substrates12 and 14, then the construction of FIGS. 3A and 3B may be utilized intandem for the construction shown in FIGS. 4A and 4B. On the other hand,if one or more of the devices 22, 142 are spaced apart slightly from therespective substrates 12 and 14 so as to define respective chambers 144and 148, gasses having a high thermal conductivity may be containedwithin chambers 144 and 148 so as to facilitate the transfer of heatfrom the electrochromic devices to the outside of the inner windowchamber 146. Chamber 146 would then preferably be filled with an inertinsulating gas such as argon. Chamber 146 may also be filled with aninert solvent or a free-standing gel.

For some window applications, it may be desirable to combine thefeatures of electrochromic technology with another technology such asPolymer Dispersed Liquid Crystal (PDLC) technology. The electrochromicsystems typically used for windows are good for attenuating light (andheat) transmission, but the transition times between the high and lowtransmission states are typically measured in minutes not seconds. Thetransmitted image in the low transmission state is typically clear andfree of haze and distortion. These are great attributes for a windowsystem except if complete privacy is desired. A PDLC window systemchanges from a relatively clear transmissive state to a light scatteringcloudy or opaque state. The transmission times from clear to opaque aremeasured in seconds not minutes. If privacy is desired, the attributesof a PDLC may be preferred, but since the PDLC window just scatterslight in the opaque state, it is very poor at attenuating the totalamount of light (and heat) that is transmitted through the window. Ifprivacy and light and heat attenuation is desired, it is preferred tocombine the two technologies. A PDLC film constructed in a conventionalmanner could be laminated to an electrochromic window device or thedevices could share a substrate in a three-substrate device(substrate/electrochromic layer/substrate/PDLC layer/substrate). ThePDLC and electrochromic layers could be operated separately orsimultaneously. The PDLC layer could be oriented in front of theelectrochromic layer such that it first scatters the direct sunlightwhich is then absorbed by the electrochromic layer or the electrochromiclayer could be oriented first. The PDLC layer may contain an UV absorberto protect the electrochromic layer if it is oriented closer tosubstrate 12.

By providing a second electrochromic or electro-optic device closer tothe inside substrate 14 of window assembly 140, heat from the incidentsolar energy may be transmitted to the inside of the house rather thanthe outside of the house during winter months and colder days whereasheat can be rejected by utilizing electrochromic device 22 during thesummer months and warmer days. Optionally, the two devices can attenuatedifferent wavelengths of light, for example, visible and NIR. Further,one of the two devices 22 and 142 could be used at any one time.Nevertheless, it would also be possible to simultaneously activate bothdevices 22 and 142, particularly during summer months, to provideadditional absorption of solar light that would otherwise be transmittedthrough the structure. Such simultaneous activation may also be desiredat nighttime for purposes of added privacy. The placement of the layer46 in this embodiment will be somewhat different than has been discussedpreviously. If an UV filter or NIR absorbing layer is used, it againwould be disposed on surface 12 a, 12 b, or 22 a in order to blockradiation. The placement of the low-E coating would be somewhatdifferent than in the previous discussion since the construction of FIG.4A is designed to enhance the heat retained inside the building duringthe winter months and colder days. The low-E coating would be disposedon surfaces 22 b or 142 a to reject the heat from the outside during thecooling seasons and to retain heat during the heating seasons.

FIG. 4B shows a variation of the spacer construction for a dual-elementwindow in which spacer 124 extends across the tops of elements 22 and142 rather than in between elements 22 and 142 as in the constructionshown in FIG. 4A.

As discussed above, a benefit of maintaining the electrochromic devicewithin the airtight chamber of the insulated glass unit is that a firstseal 36 (206 in FIGS. 5 and 6A-6I) need not be highly impermeable tooxygen and moisture, and need not be further cured after originalmanufacture of the electrochromic device. An example of a preferredmaterial is EPDM that may be preformed as a gasket that is subsequentlyadhered to the surface of a transparent substrate 202 (see FIGS. 5 and6A). Transparent substrate 202 is coated with a transparent electrode204. In addition, an adhesive may be applied in advance to the oppositesurface of seal 206 and a release liner 208 may be applied to theadhesive such that the subassembly 200 shown in FIG. 5 may bepreassembled and stored in inventory. Previously, such a preassembledsubassembly for an electrochromic device could not be constructed due tothe materials that were required to be used for the seal.

It should be noted that the drawings discussed above and below are notto scale, but have exaggerated dimensions in some respects, particularlyin their thicknesses, to illustrate the principles of the invention. Itshould be understood that certain aspects of the invention may beapplied to smaller electrochromic devices, such as electrochromicrearview mirrors.

The inventive method for constructing an electrochromic device of thetype that may be implemented in a large electrochromic window assemblyis discussed below with reference to FIGS. 6A-6I. As illustrated in FIG.6A, a subassembly 200 (see also FIG. 5) is constructed whereby a sealgasket 206 is adhesively attached or bonded to the surface of atransparent electrode layer 204 that is formed on a transparentsubstrate 202. Transparent glass substrates having a preapplied layer ofa transparent electrode are commercially available, such as TEC-15 glassfrom Libbey-Owens-Ford. As illustrated in FIG. 6A, a release liner 208,such as polyethylene or siliconized polyester or the like, may beapplied to the opposite surface of seal gasket 206. Release liner 208could be secured to seal gasket 206 by the same adhesive that wouldsubsequently be used to secure a second transparent substrate 210 havinga transparent electrode layer 212 formed thereon (see FIG. 6B).

Conceivably, seal gasket 206 could be preconstructed to have adhesiveapplied to its two opposite surfaces and release liners may be appliedto both surfaces of seal gasket 206. This would allow the seal gasketsby themselves to be separately stored, then selected and readily appliedonto one of the coated substrates 202 or 210. Because seal gasket 206has sufficient resistance to compression to maintain cell spacing whileextending around substantially the entire periphery of the transparentsubstrates, seal gasket 206 functions as a spacer both during and afterthe manufacturing process.

As shown in FIG. 6B, once release liner 208 has been removed from sealgasket 206, a second subassembly 213 including a second transparentsubstrate 210, having one surface coated with a transparent electricallyconductive material 212, may be aligned with transparent substrate 202and pressed into contact with the adhesive on seal gasket 206. Thisoperation may be performed with substrates 210 and 202 disposed ineither horizontal planes or vertical planes. An apparatus such as avacuum chuck or the like may be used to move substrates 212 and 202together. Once coated substrates 202 and 210 are pressed into contactvia seal gasket 206, a secondary seal may be applied and the chamberdefined between coated substrates 202 and 210 and seal gasket 206 may befilled with an electrochromic medium 215. Preferably, the electrochromicmedium contains a gelling agent that will form a cross-linked polymermatrix between coated substrates 202 and 210. Substrates 202 and 210 maybe held in place by the vacuum chuck that first holds the substrates ina fixed position until the chamber is filled with the electrochromicmedium. Once the matrix has been formed, the assembly will exhibitsufficient structural integrity such that one of the substrates will notbow towards the other substrate in a middle portion of the device andthe spacing between the substrates will be maintained uniform throughoutthe device.

Additionally, the first seal may be dispensed and include variousrheology modifiers to adjust the flow characteristics of the dispensedmaterial. Other additives could be used to affect other chemical,physical, or aesthetic properties. To maintain the desired cell spacingwhen a dispensed material is employed, the spaced apart relationship ofthe substrates 28 and 30 could be maintained by the use of certainspacers consisting of, for example, glass spheres, synthetic spheres,rubber blocks, and the like.

As shown in FIG. 6C, coated substrate 210 preferably includes a fillhole 214 into which the electrochromic material is introduced. Anadditional aperture (not shown) may also be formed to enable a vacuum tobe attached and hence to allow vacuum enhanced filling of the chamberbetween the two substrates. The fill hole 214 is preferably conicallyshaped with the larger opening disposed at the exterior of the device.The conical hole is formed by drilling partially from each side of theglass lite to avoid the uneven breakthrough and shattering seen whensuch a hole is drilled from one side only. After the introduction ofelectrochromic material into the device, the fill hole(s) is plugged(sealed) with some type of material that will not adversely affect theelectrochromic material. This material may be a polymeric material suchas polyisobutylene, polyolefin, butylnitrile and the like.Alternatively, this material may be a pliable or rigid sphere orspheroid whose size is selected to fit within the conical hole withoutdropping into the space formed by the two spaced-apart glass elements.This sphere or spheroid may be made of glass, Teflon®(tetrafluoroethylene fluorocarbon, fluorinated ethylene-propylene, orcopolymers thereof), or the like. Preferably, the sphere is a Teflon®ball obtained from Small Parts Inc. The material utilized as the conicalhole sealant may also be held in place by an adhesive material. Thismaterial may be a pressure sensitive adhesive or a UV curable material,preferably Dyamx 20014. A glass or plastic slide may also besuperimposed upon the adhesive as an additional sealing material. In thecase of a UV curable adhesive, the slide is positioned over the pluggedconical hole prior to the curing of the adhesive.

During filling, the structure shown in FIG. 6C may be rotated from avertical orientation with fill hole 214 at the top portion of thestructure so as to use gravity to aid filling, to a horizontal position.Rotation about another axis simultaneously is also possible. Thisprevents air bubbles from getting trapped in the chamber. By formingfill hole 214 in a conical shape, a ball 216 may subsequently beinserted into fill hole 214 after filling has been completed (see FIG.6D). The chosen shape of fill hole 214 serves to prevent plug 216 fromfalling through substrate 210 into chamber 215 and allows for the plugto have a preformed shape, such as spherical, conical, etc. Again, thedimensions of fill hole 214 and ball 216 relative to the electrochromicdevice structure shown in the figures is exaggerated for purposes ofillustration. In general, fill hole 214 and ball 216 would be extremelysmall when compared to the entire surface area of the electrochromicdevice.

Fill hole 214 is preferably formed near the perimeter of theelectrochromic device in an area just lying inside of the sealed area ofthe chamber. In this manner, the fill hole and plug will not be highlyvisible to someone looking through the window and may be obscured by theframe or spacer used to hold the electrochromic device within the windowstructure.

Plug 216 is preferably made of a material that will not poison orinteract with the electrochromic medium contained in chamber 215. Morespecifically, plug 216 is preferably spherical in shape and made ofmaterials such that when the plug is inserted in hole 214, it snugglyfits within fill hole 214. Plug 216 may be made of polyethylene,Teflon®, stainless steel, gold, glass, ceramic, polypropylene,polyamide, PIB, butyl rubber or EPDM. As shown in FIG. 6E, after plug216 has been inserted into fill hole 214, an adhesive 218 is applied tothe top of plug 216 so as to slightly overfill fill hole 214.Preferably, UV curable adhesive is Dymax 20014. By utilizing a plug 216or any other similar structure that could fill a fill hole of virtuallythe same shape in a similar manner, adhesive 218 is prevented fromcoming into contact with the electrochromic material disposed withinchamber 215. This is important, since many of the adhesives interactwith, or otherwise poison, electrochromic materials that are commonlyused for electrochromic devices. Subsequently, a thin transparent member220 is pressed down onto adhesive 218 until it essentially lies flat onthe outer surface of coated substrate 210 as illustrated in FIG. 6F.Member 220 is preferably made of a material that is transparent to UVradiation and that is also impermeable to oxygen. Member 220 may be madeof Mylar or a glass microscope slide slip cover. Member 220 ispreferably dimensioned to be sufficiently larger than the opening offill hole 214 so as to increase the path that oxygen or moisture wouldneed to travel to enter the device through fill hole 214.

Then, as illustrated in FIG. 6F, UV radiation 222 is directed onto andthrough member 220 so as to cure adhesive 218. Once adhesive 218 hascured, a very strong plug for fill hole 214 is created without utilizingany highly visible plug for the fill hole.

FIG. 6G shows the next step in the process, which is to apply bus clips40 a and 40 b to coated substrates 210 and 202. Such clips are generallyfriction fit around the perimeter of the electrochromic device.

In prior constructions, particularly in electrochromic devices used asrearview mirrors, two separate bus clips were typically applied alongopposite edges of the electrochromic device so as to avoid inadvertentcontact and electrical shorting between the bus clips. Thus, forexample, prior electrochromic devices would include bus clips positionedsuch as in location 41 a and 41 b shown in FIG. 6G with substrates 210and 202 offset from each other. Furthermore, such bus clips would onlyextend along a top or bottom edge of the electrochromic device, sincethe distance through which the current would flow was not excessivelygreat. With larger scale electrochromic devices such as those used inwindows, the distance between the bus clips and the opposite edge of thecorresponding transparent electrode tends to cause non-uniform currentflow through the transparent electrodes. Such non-uniform current flowcauses non-uniform coloration of the electrochromic material, which canbe aesthetically undesirable.

Previously, bus clips were conventionally formed of a metal strip orspine with a plurality of resilient fingers extending transversely fromthe spine. As an example, with reference to FIG. 6H, conventional busclips included a spine 230 a and a plurality of spaced-apart resilientfingers 226 a and 228 a that extend transversely from the spine. Asshown in FIG. 6G, such clips would have fingers that are taperedslightly inward so as to clamp onto the outer periphery of the coatedsubstrates. In general, in conventional bus clips, fingers 226 a and 228a had widths that were much greater than the spacings between each ofthe fingers. Thus, the fingers extending from a conventional spine 230 ahad the same appearance on both sides thereof as fingers 226 a shown inFIG. 6H. The inventive bus clips, on the other hand, differ from theconventional bus clips insofar as every other finger on at least one ofthe sides of the bus clip is removed or otherwise not provided so as toallow a bus clip on the other substrate to be applied along the sameedges without making physical or electrical contact with the fingers ofthe other bus clip. Thus, the fingers have widths that are less than thespacing therebetween to allow the fingers of the two bus clips 40 a and40 b to be effectively intermeshed at least in those regions where thefingers of opposing bus clips extend towards one another.

As shown in FIGS. 10A and 10B, the spacing or pitch between fingers 228should be greater than the width of fingers 228 themselves to allow forbending the bus clip around the corners of the substrates withoutinadvertent contact that would cause a short. Likewise the length of thefingers should be selected to also prevent such shorting. As shown inFIG. 10C, fingers 226 and 228 may have dimples 400 so as to providebetter electrical contact with the transparent electrodes.

By utilizing the inventive bus clip structure shown in FIGS. 6H, 10A,and 10B, bus clips may be provided about the entire periphery of bothcoated transparent substrates 210 and 202 without making physicalcontact with one another. Thus, by enabling bus clips to be providedaround the entire periphery of the electrochromic device and hencecontact the respective transparent electrodes 204 and 212 about theirentire perimeters, the transparent electrodes will show a more uniformcurrent density throughout the surface of the electrochromic device andthe electrochromic medium will color more uniformly to its darkenedstate and be less prone to segregation than prior configurations. Toensure that the bus clips do not slide along the edge of the substratesand come into contact with one another, and to provide a second sealthat may have better moisture and oxygen impermeability properties, anepoxy sealant (not shown) may be applied to the outer perimeter of theelectrochromic device . This epoxy sealant may be applied prior tofilling of the window or it may be applied at the time during which theelectrochromic device is secured within a groove of an insulated glassspacer member or between spacer members.

Another advantage of the inventive construction is that bus clips 40 aand 40 b may be constructed of materials previously not consideredsuitable for an electrochromic device. In particular, steel or otheriron containing elements were not previously considered for use as busclips due to the fact that such materials will rust as a result ofsurface oxidation when exposed to oxygen. However, by protecting theentire electrochromic device structure within an airtight chamberbetween the two substrates of the insulated glass assembly, and byfurther filling the chambers with inert gas such as argon, bus clipsmade of steel or the like will not be exposed to oxygen and will thusnot rust. Steel clips are preferable to conventional clip materials,since they are roughly one-fifth of the cost. Because it is preferableto extend the bus clips around the entire periphery of theelectrochromic device, this cost savings is all the more significant.

FIG. 7 shows an alternative construction for extending electricalconductors in contact with the respective transparent electrodes 204 and212 about their entire perimeter. Specifically, in FIG. 7, two exposedwires 235 a and 235 b are pressed into opposite sides of seal gasket206. The adhesive that is applied to the seal gasket serves to hold thewires in place as the wires are extended around the perimeter of sealgasket 206. This assembly may then be adhered and pressed against therespective transparent electrodes 204 and 212, and thereby providecontact with electrical wires 235 a and 235 b about the entire perimeterof electrodes 204 and 212. A similar approach shown in FIG. 8 may betaken using conductive foil strips 240 a and 240 b that may be adheredto opposite sides of seal gasket 206. A conductive adhesive layer couldthen be applied to the exposed surfaces of the metal foil to adhere totransparent electrodes 204 and 212. The conductive foil strips could beapplied on the inside or outside of the transparent elements and alsocould be applied by vacuum depositing a conductive metal around theperimeter of the device.

It should be noted that while the manufacturing method discussed aboveis described with respect to electrochromic devices for incorporationinto windows, such a method may be applied to electrochromic devices oreven other devices providing variable light transmittance. For example,such a method could be used to construct electrochromic rearviewmirrors. Further, the inventive fill hole and plugging structure mayalso be utilized in an electrochromic mirror as may the inventive busclip construction described above. Further, while specific windowassemblies are described above with respect to FIGS. 1-4, the inventiveelectrochromic device may be incorporated into any other known windowstructure.

It should also be noted that a photovoltaic power source mayadditionally be added to the above window structures as disclosed inU.S. Pat. No. 5,805,330. The photovoltaic source may be used to powerthe electrochromic device.

FIG. 9 shows an embodiment of the window assembly that includes acontrol mechanism for monitoring the light levels transmitted throughelectrochromic device 22 and for adjusting the voltage level applied toelectrochromic device 22 so as to vary its transmittance and therebymaintain a constant level of light in the interior of the building. Thissystem includes a photo sensor 300 that may be a part of a photovoltaicpower source that is mounted within chamber 26 behind electrochromicdevice 22. By mounting photo sensor 300 behind electrochromic device 22,the sensor may sense the light level as attenuated by electrochromicdevice 22 and thereby adjust its transmittance/absorptioncharacteristics so as to maintain a uniform intensity of light as sensedby the sensor. The circuitry for controlling the voltage applied toelectrochromic device 22 may also be incorporated within chamber 22 orotherwise incorporated within the frame/spacer assembly. If photosensor300 is part of a photovoltaic power supply, then the voltage that is tobe supplied to electrochromic device 22 may be generated from within thewindow assembly itself.

As also shown in FIG. 9, a manual switch mechanism 302 may be suppliedon the outside of transparent substrate 14 that allows a person toeffectively dial the desired transmittance level. Switch 302 may supplythis signal to the circuitry and to photosensor 300 via a magnetic linkthrough glass 14 in a similar manner to which signals are transmittedthrough automotive glass in cellular telephone antennas. Thetransmittance level of electrochromic device 22 may also be controlledremotely using a wireless receiver that is contained within chamber 26.The wireless receiver may be an infrared sensing photodiode or the likeso as to receive an infrared control signal from a remote transmitter.The receiver may also be a radio frequency receiver. In this manner, thetransmittance levels of the windows may be remotely controlled using aremote control transmitter. Also, the transmittance of the windows maybe adjusted under control of a microprocessor-based system remote fromthe windows that may send control signals via an X10-type system throughthe commercial power lines of the building in which the windows aremounted.

A preferred electrical control system and electrical contacts forcoupling the electrochromic window to the electrical control system isdisclosed in commonly-assigned U.S patent application Ser. No.09/624,792 entitled “SYSTEM TO INTERCONNECT, LINK, AND CONTROL VARIABLETRANSMISSION WINDOWS AND VARIABLE TRANSMISSION WINDOW CONSTRUCTIONS,”and filed on the same date as this application, the entire disclosure ofwhich is incorporated herein by reference.

As noted above, color instability has been a drawback of prior artelectrochromic windows. That is, when these windows have been exposed tooutdoor weathering conditions, high temperatures, and UV radiation, forextended periods of time in both their inactivated and activated states,or cycled, unacceptable changes in the color of these windows haveoccurred. Additionally, accelerated testing for electrochromic windowsto predict the field life of a device in a relatively short period oftime, has generally used the change in absorbance at a given wavelength,or the percent of white light transmitted as a figure of merit inevaluating electrochromic devices after a series of tests. These values,while being easily measured, may not be related to consumeracceptability, that is, a small change in the absorbance at a chosenwavelength does not give any information about changes at any otherwavelength. Also, the use of percent light transmission may be similarlymisleading or incomplete as an indication of the acceptability of anelectrochromic window. The change in the value of color coordinates as afigure of merit is more useful in evaluating electrochromic windows thanthe methods previously used. Also, this measured color change is a moresensitive measure of perceived appearance than either percent lighttransmission or absorbance change at a given wavelength.

In accordance with the present invention, electrochromic devices aredisclosed that exhibit superior color stability, in addition, astraightforward, relatively short time test methods for evaluatingvarious electrochromic device designs and constructions for suitabilityare disclosed.

First, an electrochromic device to be evaluated is constructed using thecombination of materials, solvents, polymerizing agents, etc. desired.After construction, the light transmitted through an electrochromicdevice is measured and recorded in the L*a*b* color space. The device isthen exposed to simulated sunlight conditions in a weathering chamberfor a period of at least 600 to 700 hours while cycling between its hightransmittance state and its low transmittance state, being held in itslow transmittance state for at least 30 percent of the total exposuretime. After the exposure, the color of the transmitted light is againmeasured and the difference between the color coordinates for both theclear and colored state are calculated. It has been found that devicesthat have a color change of less than five after this exposure exhibitenhanced color stability when exposed to outdoor weather conditionsafter prolonged periods, greater than two years.

Second, a device after fabrication, is cycled while exposed to anelevated temperature of 85° C. for a period of 1000 hours, the colorcoordinates are also recorded before and after this exposure. In thiscase also, a color change of five or less is indicative of thecapability of similarly constructed devices to withstand prolongedoutdoor exposure. The use of ten as an upper limit for the color changein evaluating electrochromic windows may seem arbitrary, however, afterevaluation of a number of windows, it is believed that this color changeis approximately the limit for customer acceptance for aging ofelectrochromic windows. That is, if a window were required to bereplaced due to breakage, or for some other reason, the replacementwindow would be similar in appearance to the aged windows. A colorchange of five or less is believed to be required for broad customeracceptance of the difference between an aged window and a new one. Morepreferably, a color change of one or less will generally give agedwindows whose color is generally indistinguishable from a new window bypeople with normal color vision.

In the above discussion and the following examples, references are madeto the spectral properties of electrochromic windows constructed inaccordance with the parameters specified in each of the examples. Indiscussing colors, it is useful to refer to the CommissionInternationale de I'Eclairage's (CIE) 1976 CIELAB Chromaticity Diagram(commonly referred to as the L*a*b* chart). The technology of color isrelatively complex, but a fairly comprehensive discussion is given by F.W. Billmeyer and M. Saltzman in Principles of Color Technology, 2ndEdition, J. Wiley and Sons Inc. (1981), and the present disclosure, asit relates to color technology and terminology, generally follows thatdiscussion. In the L*a*b* space, L* defines lightness with an L* valueof 100 being white and a L* value of 0 being black, a* denotes thered/green value with a positive a* indicating red and a negative a*indicating green, and b* denotes the yellow/blue value with a positiveb* indicating yellow and a negative b* indicating blue. Each of theelectrochromic media has an absorption spectra at each particularvoltage from which the L*a*b* values may be calculated. To calculate aset of color coordinates, such as L*a*b* values, from the spectraltransmission or reflectance, two additional items are required. One isthe spectral power distribution of the source or illuminant. The presentdisclosure uses CIE Standard Illuminant D₆₅. The second item needed isthe spectral response of the observer. The present disclosure uses the2-degree CIE standard observer. The illuminant/observer combination usedis represented as D65/2 degree. The value ΔE is equal to the square rootof (L_(f)*−L_(i)*)²+(a_(f)*−a_(i)*)²+(b_(f)*−b_(i)*)² where the “i”subscript denotes the initial values of the color coordinate values andthe “f” subscript denotes the color coordinate values after testing, andhence, provides a measure for quantifying color stability. For anelectrochromic window color stability, the ΔE value of the window shouldbe less than 10. Preferably, the ΔE value is less than 5, and morepreferably is less than about 1.

To illustrate the properties and advantages of the present invention,examples are provided below. The following illustrative examples are notintended to limit the scope of the present invention, but to illustrateits application and use. In the examples below, each of theelectrochromic windows was constructed in the same conventional manner.Specifically, two pieces of glass coated with a transparent conductivecoating (TEC-15 glass from Libbey-Owens-Ford) were held in aspaced-apart relationship with an epoxy seal material containing glassbeads with 250 mm diameter. A gap was left in the seal for theintroduction of the electrochromic medium into the cell via vacuumbackfilling. The gap was plugged with a UV-curable material afterbackfilling.

Specifically, 2 by 5 windows refer to devices constructed with twopieces of glass each approximately 2 inches by 5 inches coated with atransparent conductive coating (unless otherwise noted TEC-15 glass fromLibbey-Owens-Ford) were held in a spaced-apart relationship with a sealmaterial containing spacers, for example, glass beads with a specificdiameter. A gap was left in the seal for the introduction of theelectrochromic medium into the device via vacuum backfilling. The gapwas then plugged.

EXAMPLE 1

Two of the above constructed windows were filled with a solutioncontaining 16 mM dimethyl-4,4′-bipyridinium bis(tetrafluoroborate); 16mM 5, 10-dihydro-5, 10-dimethyl phenazine and 30 mM4′-methyl-2′-hydroxy-phenyl-benzotriazole (Tinuvin P) in propylenecarbonate (PC) with 3 wt % polymethyl methacrylate (PMMA). The colorcoordinates (L*a*b* D65/2°) of transmitted light were recorded and thewindows were then subjected to 730 hours of high intensity UV light inan Atlas Weather-Ometer with an Xe lamp operating at 0.55 W/m² at 340 nm(a darkening cycle consisting of operation of the device at 1.2V for 20sec. and at 0.0V for 40 sec., these times allowed for the devices toundergo darkening to their steady state transmission values and allowthe devices to clear completely). The color coordinates were againrecorded and the difference (ΔE) for the windows in their hightransmission condition was 2.50 and 2.22 for the low transmissioncondition ΔE was 4.45 and 4.99.

EXAMPLE 2

Two windows were constructed the same as in Example 1, but were filledwith 16 mM bis (2-phenyl ethyl)-4,4′-bipyridinium bis (tetrafloroborate)16 mM DMP, 30 mM Tinuvin P in PC with 3 wt % PMMA. A similar test asperformed to Example 1 was performed except that the windows weremeasured after 629 hours. These windows exhibited a ΔE (hightransmission) of 1.18 and 1.121 and a ΔE (low transmission) of 1.09 and1.33.

EXAMPLE 3

Two windows were constructed having the same structure as in Examples 1and 2 above except that the windows were filled with 15 mM bis (3-phenylpropyl)-4,4′-bipyridinium bis (tetrafluoroborate), 16 mM DMP 30 mMTinuvin P in PC with 3 wt % PMMA after 629 hours, which is aconventional electrochromic material. Accordingly, this example servedas a control for purposes of comparison with Examples 1 and 2 above. Thefollowing measurements were made after 629 hours in the Weather-Ometer.Specifically, the conventional window exhibited a ΔE (high transmission)of 6.72 and 9.93 and a ΔE (low transmission) of 7.50 and 10.01.

EXAMPLE 4

Two windows similar to examples 1-3 were constructed except they werefilled with 16 mM dimethyl-4,4′-bipyridinium bis(tetra-fluoroborate); 8mM 5,5′, 10,10′-tetrahydro, 5,5′,10,10′-tetramethyl-2,2′-biphenazine; 30mM Tinuvin P in PC with 3 wt % PMMA. A similar test as used in Example 1above was performed except that the measurement was taken after 691hours. These windows exhibited a ΔE (high transmission) of 4.00 and 3.74and a ΔE (low transmission) of 4.10 and 3.60.

EXAMPLE 5

Two windows were constructed in the same manner as in Example 1 and theywere filled with the same material. These windows were then subjected tocontinuous cycling outdoors at an angle at 5° from a horizontalcondition. After approximately two years outdoors and 1.14 millioncycles, the color coordinates were measured, and the ΔE (hightransmission) values were determined to be approximately 7.34 and 9.00and the ΔE (low transmission) values were determined to be 6.41 and4.21.

EXAMPLE 6

Two windows were constructed and filled in the same manner as in Example2 above. They were also filled with the same materials disclosed inExample 2. These windows were then subjected to continuous cyclingoutdoors at an angle of 5° from a horizontal condition. Afterapproximately 1.11 million cycles, the windows exhibited a ΔE (hightransmission) of 2.88 and 6.05, and a ΔE (low transmission) of 5.77 and5.15.

EXAMPLE 7

Two conventional electrochromic windows were constructed in the samemanner as in Example 3 above and filled with the same conventionalelectrochromic material. These windows were then continuously cycledoutdoors at an angle of 5° from a horizontal condition. After about 1.11million darkening cycles, these windows exhibited a ΔE (hightransmission) of 29.97 and 22.25 and a ΔE (low transmission) of 26.21and 20.35.

EXAMPLE 8

Electrochromic window devices were fabricated from two sheets of glasscoated with a transparent conductive layer (TEC 15 glass, Libbey OwensFord) and measuring approximately 2 inch by 5 inch. These substrateswere bonded together by an epoxy perimeter seal containing a small gapfor subsequent filling, with the conductive surfaces facing each otherin a parallel, spaced-apart manner. The spacing between the electrodeswas controlled by the use of spacer beads in the epoxy seal and measuredapproximately 250 microns. The substrates were offset from each otherslightly to allow for electrical contact. The devices were then filledby standard vacuum backfilling techniques through a small fill port leftin the perimeter seal with a solution comprising 34 mM methylviologenbis(tetrafluoroborate), 21.8 mM(6-(tetra-t-butylferrocenyl)hexy)triethylammonium tetrafluoroborate, 2mM (6-(tetra-t-butylferrocenium)hexy)triethylammoniumbis(tetrafluoroborate), 30 mM2-(2′-hydroxy-5′-methylphenyl)-benzotriazole (Tinuvin P, Ciba Geigy),and 50 mM 2-(2′-hydroxy-3′-t-butyl-5′-n-pentylpropionate)-benzotriazolein a solution of 3% by weight polymethylmethacrylate (Elvacite™ 2051) inpropylene carbonate. The fill port was then plugged with a UV curableadhesive and cured by exposure to UV light.

The electrochromic windows were then placed in an Atlas Ci-65Weather-ometer for accelerated durability testing. Operating parametersfor the Weather-ometer were set to provide continuous irradiation (0.55W/m² at 340 nm) with a black panel temperature of ca. 70° C. and 47° C.ambient. The windows were cycled continuously between their hightransmittance and low transmittance states. Each cycle consisted ofapplication of 1.2 V DC for 30 seconds and application of 0 V for 30seconds. Color coordinates (L*a*b* values) of each window were measuredat approximately one week intervals in order to monitor color changes;the color changes, ΔE, for one of the devices in its high transmissionstate are shown in Table 1 below.

TABLE 1 Hours Color Change   0 0.00  263 1.09  489 0.47  648 0.53  7640.56  926 0.58 1091 1.34 1211 0.83 1354 1.17 1562 1.31 1709 0.90 19361.03 2105 1.14 2292 1.32 2509 1.38 2751 1.59 2926 1.33 3069 1.56 32151.57 3406 1.68 3819 2.27 3983 2.13 4146 2.04 4389 2.26 4628 1.91 47972.40 4963 2.41 5144 2.49 5360 2.06 5598 2.04 5821 2.13 5987 2.16 61902.21 6361 2.30 6545 2.27 6785 2.48 7010 2.90 7211 2.58 7401 2.42 75862.45 7677 2.26 7819 2.65 7946 3.00 8088 2.82 8231 4.94 8374 4.47 85174.37

EXAMPLE 9

Electrochromic window devices were fabricated as in the previousexample. These devices were then filled as above with a solutioncomprising 34 mM octylviologen bis(tetrafluoroborate), 21.8 mM(6-(tetra-t-butylferocenyl)hexyl)triethylferrocenyl)hexyl)triethylammoniumtetrafluoroborate, 2 mM(6-(tetra-t-butylferrocenium)hexyl)triethylammoniumbis(tetrafluoroborate), 30 mM2-(2′-hydroxy-5′-methylphenyl)-benzotriazole (Tinuvin P, Ciba Geigy),and 50 mM 2-(2′-hydroxy-3′-t-butyl-5′-n-pentylpropionate)-benzotriazolein a solution of 7% by weight of a 1:10 isocyanatoethylmethacrylate/methyl methacrylate copolymer in propylene carbonate. Thesolution also included Bisphenol A as a crosslinking agent in a 1.45 to1 molar ratio of Bisphenol A to isocyanate functionality on thecopolymer and 250 ppm of dibutyltin dilaurate as catalyst.

An electrochromic window was then placed in an Atlas Ci-65Weather-ometer for accelerated durability testing. Operating parametersfor the Weather-ometer were set to provide continuous irradiation (1.10W/m² at 340 nm) with a black panel temperature of ca. 75° C. and 55° C.ambient. The window was cycled continuously between its hightransmittance and low transmittance states. Each cycle consisted ofapplication of 1.2 V DC for 20 seconds and aplication of 0 V DC for 40seconds. Color coordinates (L*a*b* values) of the window were measuredat approximately one week intervals in order to monitor color changes;the color change for one of the devices in its high transmission stateare shown in Table 2 below.

TABLE 2 Hours Color Change   0 0.00  285 3.02  990 2.72 1133 2.43 12922.83 1434 3.22 1578 4.66 1719 5.17 1862 3.02

EXAMPLE 10

Electrochromic window devices were fabricated in a similar fashion tothat described in Example 8 above except that the external dimensions ofthe windows were 5 inch by 5 inch and the spacing between the front andrear electrodes was maintained at approximately 760 microns. Theperimeter seal of these devices was composed of an inner seal and anambient cure epoxy outer seal. No gap was provided in the seal; rather,the devices were filled via standard vacuum backfilling techniquesthrough a small conical fill port drilled through the face of one theglass plates. The fill solution comprised 4mM5,10-dimethyl-5,10-dihydrophenazine, 6 mM octylviologenbis(tetrafluoroborate), 30 mM2-(2′-hydroxy-5′-methylphenyl)-benzotriazole (Tinuvin P, Ciba Geigy),and 50mM 2-(2′-hydroxy-3′-t-butyl-5′-n-pentylpropionate)-benzotriazolein a solution of 8% by weight of a 1:10 isocyanatoethylmethacrylate/methyl methacrylate copolymer in propylene carbonate. Thesolution also included Bisphenol A as a crosslinking agent in a 1.45 to1 molar ratio of Bisphenol A to isocyanate functionality on thecopolymer. After the fill was complete, a small teflon ball was pressedin the fill port and a thin glass slide measuring approximately 0.5 inchby 0.5 inch was attached as a cover plate over the fill hole using aUV-curable adhesive.

The electrochromic windows were then placed in an oven at 85° C. foraccelerated durability testing. Color coordinates (L*a*b* values) of thewindow were measured at approximately one week intervals in order tomonitor color changes; the color change for one of the devices in itshigh transmission state are shown in Table 3 below.

TABLE 3 Hours Color Change   0 0.00  88 4.30  157 5.11  245 5.65  3145.84  403 5.96  563 7.25  755 6.69  899 6.38 1067 6.69 1427 7.44 17047.91 1864 8.09 2024 8.36 2185 8.75 2345 9.12 2515 9.74 2656 9.48 28169.82 3224 9.93

As evident from the above examples, the novel electrochromic materialsexhibited signifgicantly improved color stability.

The above description is considered that of the preferred embodimentsonly. Modifications of the invention will occur to those skilled in theart and to those who make or use the invention. Therefore, it isunderstood that the embodiments shown in the drawings and describedabove are merely for illustrative purposes and not intended to limit thescope of the invention, which is defined by the following claims asinterpreted according to the principles of patent law, including thedoctrine of equivalents.

The invention claimed is:
 1. A window comprising an electrochromicmedium having a color stability ΔE less than 5, measured in its minimumlow transmission state after exposure to 700 hours in a weatherometerwhile cycling, each cycle consisting of application of sufficientpotential for a sufficient time such that the window reaches its lowtransmission state for at least 210 hours.
 2. The window of claim 1,wherein each cycle consists of applying a voltage of about 1.2V for 20sec. and 0.0V for 40 sec.
 3. The window of claim 1, wherein saidelectrochromic medium is dispersed in a cross-linked polymer matrix. 4.A window comprising an electrochromic medium having a color stability ΔEless than 5, measured in its high transmission state after exposure to700 hours in a weatherometer while cycling, each cycle consisting ofapplication of sufficient potential for a sufficient time such that thewindow reaches its low transmission state for at least 210 hours.
 5. Thewindow of claim 4, wherein each cycle consists of applying a voltage ofabout 1.2V for 20 sec. and 0.0V for 40 sec.
 6. The window of claim 4,wherein said electrochromic medium is dispersed in a cross-linkedpolymer matrix.
 7. A window comprising an electrochromic medium having acolor stability ΔE less than 5, measured in its low transmission stateafter exposure to 700 hours in a weatherometer while cycling, and acolor stability ΔE less than 5, measured in its high transmission stateafter exposure to 700 hours in a weatherometer while cycling, whereineach cycle consists of application of sufficient potential for asufficient time such that the window reaches its low transmission statefor at least 210 hours.
 8. The window of claim 7, wherein each cycleconsists of applying a voltage of about 1.2V for 20 sec. and 0.0V for 40sec.
 9. The window of claim 7, wherein said electrochromic medium isdispersed in a cross-linked polymer matrix.